This paper presents the design of a dual-polarized frequency-modulated continuous wave (FMCW) radar system with a coupler-integrated lens antenna for automotive synthetic aperture radar (SAR) applications. High-resolution radar imaging is imperative for automotive use, with dual-polarized SAR imaging providing robust support in achieving this objective. However, exploration of the system design for dual-polarized FMCW SAR systems has been limited. The paper outlines the design of the aforementioned radar system, emphasizing its suitability for automotive SAR applications. It details the requisite parameters for dual-polarized automotive SAR systems and the design considerations for the dual-polarized lens antenna. Additionally, it proposes a radar signal monitoring method employing a coupler-integrated antenna to detect the radiated radar signal. Furthermore, a dual-polarization synthesis method is introduced to enhance SAR image quality. Experimental validation of the implemented dual-polarized FMCW radar with a coupler-integrated lens antenna confirms the effectiveness of the proposed system design.

This paper presents a curved-retrodirective beamforming system for improving microwave power transmission efficiency in the Fresnel region. Since microwave power transmission in the far-field region has very low efficiency, studies on the Fresnel region are being actively conducted. In these studies, a retrodirective beamforming (RDB) technique is popular. The RDB system with a sub-array structure was a realistic structure that reduced system complexity. However, the transmission efficiency is lowered because the beamwidth of the transmitter antenna element is narrow. To solve this problem, this paper proposes a curved-retrodirective beamforming system that can focus the microwave power on the receiver. The proposed system uses the peak gain of the transmitter antenna element by using tilted beams to improve transmission efficiency. The system design method that can maximize the transmission efficiency is also presented depending on the given conditions such as transmission distance, characteristics of the transmitter and receiver antenna. The simulation showed a reduction in power leakage compared to the conventional system. The fabrication and measurement validated the efficiency improvement of the proposed system for IoT devices in the Fresnel region.

This paper proposes a millimeter-wave series-fed coupled split-ring resonator array (SCSRRA) antenna with a wide fan-beam pattern and low sidelobe level (SLL) for automotive radar. The proposed array antenna has the advantages of low cost, low profile, and low manufacturing difficulty. The proposed array antenna uses a split-ring resonator as a radiating element coupled from a microstrip line. The split-ring resonator has the advantage of suppressing cross-polarization due to feed phase errors. To reduce the surface wave through the ground edges and enhance the beamwidth, we added the mushroom-shaped electromagnetic bandgap (EBG) structure. Amplitude tapering to reduce the SLL was implemented by adjusting the distance between each element and the microstrip line. The prototype SCSRRA antennas operating at 79 GHz were fabricated, and the characteristics of the wide fan-beam pattern and low SLL were experimentally verified.

For the detection of buried targets in a dielectric medium, the decomposition of time-reversal operator (DORT) using a multistatic system has been effective in separating multiple targets and imaging their locations. Recently, nonlinear (harmonic) radar-based DORT has been introduced to detect nonlinear targets (NTs) with small radar cross sections (RCSs). However, faulty antennas (i.e., elements unable to transmit or receive signals) can distort the received multistatic response matrix, significantly degrading detection performance and accuracy, necessitating an extension of DORT to address such scenarios. This article presents double scan-DORT (DS-DORT), an extended DORT approach that ensures effective buried NT detection even in the presence of faulty antennas. Unlike conventional DORT, DS-DORT employs two arrays, each performing both transmission and reception, generating two multistatic responses that compensate for distortions caused by faulty antennas. By simultaneously retransmitting two sets of back-propagation signals derived from these responses, DS-DORT minimizes inaccuracies, maintaining robust target detection. Furthermore, DS-DORT offers practical advantages in real-world scenarios, such as hazardous/inaccessible environments, or when antenna failures occur unpredictably, without requiring additional hardware or complex algorithms. Beyond its capability to mitigate faulty antenna effects, DS-DORT also enables the reconstruction of 3-D target locations by leveraging a 2-D antenna array configuration when all antennas function correctly. The proposed approach is validated through numerical simulations and measurements, demonstrating superior detection performance compared with conventional DORT in scenarios involving single or multiple faulty antennas. The results confirm that DS-DORT enables accurate detection of buried NTs even under faulty antenna conditions.

This letter proposes an integrated lens antenna (ILA) that uses a patch as a feed structure to achieve high gain in the millimeter-wave (mmWave) band. The proposed ILA consists of a patch for feeding and an elliptical dielectric lens and can be extended from a single antenna to an array antenna. This letter covers the implementation of single ILA, 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{\times }$</tex-math></inline-formula> 1 ILA array, and 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{\times }$</tex-math></inline-formula> 1 ILA array. A series-fed network was applied for patches for low loss and small size. The proposed antenna can reduce the overall volume because it has an integrated structure without separating the lens and series-fed patch. The dielectric lens was fabricated using a 3-D printer and integrated with the printed circuit board, on which the series-fed patch was printed to implement the ILA. The simulated peak gains of single ILA, 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{\times }$</tex-math></inline-formula> 1 ILA array, and 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{\times }$</tex-math></inline-formula> 1 ILA array are 15.1, 16.6, and 18.1 dBi, respectively, while measured peak gains are 14.0, 15.3, and 16.8 dBi, respectively. The proposed 4 × 1 ILA array has a small size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\text{1.8}}\lambda _{0}\times {\text{5.1}}\lambda _{0}\times {\text{1.6}}\lambda _{0}}$</tex-math></inline-formula> due to the integrated lens design and is suitable for high frequency wireless applications as it can be easily integrated with radio frequency systems.

This paper introduces new impedance matching technique for via transition of multi-layer PCB based sub-THz antenna-in-package (AiP). In the proposed design, multiple resonating stubs are cascaded in vertical direction along via transition to create multi-stage wideband impedance matching network. The resonating stub employs rectangular ring to reduce the stub length by increasing parasitic capacitance around the ring. The impedance matching technique presented in this paper is demonstrated through design, fabrication, and measurement of subarray for the next generation’s sub-THz 6G AiP operating from 136 to 148 GHz. In the subarray design, four antenna elements are combined with 4-way power divider to form 4×1 array. The 4×1 subarray is then connected to the proposed stub-loaded via transition for input impedance matching looking from bump pad of beamforming integrated circuit. This stub-loaded via transition for impedance matching of the 4×1 subarray shows more than 17.6% fractional bandwidth (FBW) with return loss of 10 dB. Since the impedance matching network provides much wider bandwidth than the antenna element and 4-way power divider, it does not limit the 4×1 subarray performance. The designed 4×1 subarray is fabricated with advanced printed circuit board technology using modified semi-additive process. Both simulated and measured FBW of the 4×1 subarray shows more than 13.2% with return loss of 10 dB. The measured gain of the 4×1 subarray is greater than 8.9 dBi within the bandwidth.

This letter proposes an architecture for an antenna-in-package (AiP) operating at sub-terahertz (sub-THz) frequencies to improve the isolation between two ports in a dual-polarized stacked patch antenna. The design features two orthogonal fan-out lines that extend from a vertical via for probe feeding, each covered by a grounded shielding geometry. The proposed structure improves the isolation of a single element by up to 10 dB between two ports for each polarization. The performance of the proposed design was verified through simulated and measured results using a 4 × 1 subarray. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> value of the proposed 4 × 1 subarray is −20 dB at a center frequency of 145 GHz, and the measured <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> bandwidth is more than 10 GHz with a return loss of 10 dB. The measured gain within the bandwidth is higher than 9 dBi. The proposed architecture can improve the isolation and performance of sub-THz AiPs, making them viable for use in large arrays.

This article presents the novel design techniques for terahertz (THz) antenna-in-package (AiP) to overcome issues resulting from multilayer printed circuit board (PCB)-based antenna array integration, fabrication, and measurement. We propose a wideband dual-polarized stub-loaded proximity-coupled stacked patch antenna and vertical power divider as design solutions. Circuit analysis is performed to provide the equivalent circuit model and its design validity. We designed, simulated, and measured a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4 \times 1$ </tex-math></inline-formula> subarray, which ultimately builds THz <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8 \times 8$ </tex-math></inline-formula> AiP for the next generation 6G communications system. The designed proximity-coupled stacked patch antenna employs open and short stubs in via transition of the antenna’s feeding for bandwidth enhancement. The designed power divider is constructed vertically to minimize the size of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4 \times 1$ </tex-math></inline-formula> subarray. This innovative power-splitting architecture significantly decreases the complexity of the feeding network because the divider is designed without conventional T-junctions and quarter wavelength impedance transformers (ITs); thus, the size of the dual-fed dual-polarized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4 \times 1$ </tex-math></inline-formula> subarray, limited by two four-way power dividers can be shrunken considerably. Based on these proposed techniques, we fabricated and measured an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8 \times 8$ </tex-math></inline-formula> antenna array package on our custom-built probe station. The measured boresight gain of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8 \times 8$ </tex-math></inline-formula> antenna array package exceeds 17.1 dBi within the operating bandwidth of 136–148 GHz.

Vehicles to everything (V2X) communication includes a variety of types, so wide-angle scanning is integral. For wide-angle scanning, the half power beam width (HPBW) of a single antenna must be wide. Moreover, the gain, low cross-polarization level, and impedance bandwidth are essential factors in high communication performance. In this paper, a wide-angle scanning phased-array system using an arc-shorted half-elliptic patch antenna at 5.8 GHz is presented. The design of both a single antenna and the entire phased-array system are covered, and to verify the design method, the proposed single antenna and phased array system were fabricated. The proposed antenna had 162∘ HPBW in the E-plane and 8.63 dBi of peak gain. Its fractional bandwidth was 5%, and the level of cross-polarization was −16.8 dBi. Furthermore, the measured 3 dB scanning angle of the phased-array system was from −90∘ to 90∘. The proposed system has wide-angle scanning.